The axial confinement time of a single cell mirror is found to be proportional to the mirror ratio over the range of 12–74 when the mean free path for Coulomb collisions is less than one-third of the length of the device. The reduction in total end-loss current is shown to correspond to the reduction of the cross-sectional area of the plasma at the mirror throat as the mirror ratio is increased. The end-loss current density is independent of the mirror ratio and is proportional to the product of the plasma density and the acoustic speed.